I am currently house hacking in Seattle, and renting my vacant units out to lower my mortgage payment

You are in the epicenter of the Hispanic Hub of the United States. 

I intend to add a closet to the den and make it a 3 bedroom adding value as well as remodel the entire unit.

.—(1) When any lands are sold for the nonpayment of taxes, or any tax certificate is issued thereon by a governmental unit or agency or pursuant to any tax lien foreclosure proceeding, the title to the lands shall continue to be subject to any easement:(a) For conservation purposes as provided in s. 704.06 or for telephone, telegraph, pipeline, power transmission, or other public service purpose.

Total of 28 units.

But I plan on adding a 40/60 split on the next lease renewal between the two units. 

I am not new in RE (Own 2 (condo+townhome) +primary home) and all units are in San Diego and know want to buy something near beach and been in Imperial Beach lot of times love the place :)Any guidance how should i approach?

You could monitor the power usage for the two units using this device then pass through the correct billing. https://www.amazon.com/gp/prod... 

We have a large property management company our entire office uses it to manage hundreds of units.

I'm looking to scale now that there 2 units.